Natalie Portman Is Back on the Carbs After Black Swan

Natalie Portman had to change her eating habits significantly to play a prima ballerina in Black Swan, but once filming ended, so did all the dieting.

"It was just pasta and bread and pizza all the time," Portman told PEOPLE of her post-Swan diet at the film's Tuesday premiere at New York's Ziegfeld Theatre.

While filming the psychological thriller, though, a change of eating habits was key. "It wasn't really giving up [food]," Portman, 29, says. "It was just smaller portions … It was more quantity than a particular thing."

"He knows how to change when things aren't working well," Portman says of their working relationship. "Sometimes I just couldn't do something. No matter how hard I worked, I couldn't do it. He would fix it to make it something that I could do."

Praising her beau's "creativity and intelligence," the actress says, "He was really flexible. Working with film and working with actors rather than dancers, that flexibility was key."